1. Field of the Invention
The present invention relates to a cross-current type plate heat exchanger wherein fluids to be heat exchanged flow in a cross-current fashion such that one fluid flows in a direction which is at right angles to the direction of flow of the other fluid.
2. Description of the Prior Art
In a cross-current type plate heat exchanger comprising a plurality of vertically disposed heat transfer plates arranged side by side to define fluid passageways through which two fluids to be heat exchanged flow in a cross-current fashion, if cooling water is passed in a horizontal direction while vapor is passed in a vertical direction, then the film coefficient is high on the vapor side but it is kept low on the cooling water side because of its characteristics. Therefore, the overall coefficient of heat transfer is determined largely by the cooling water side and hence it is low. The cooling water which horizontally flows laterally of the heat transfer plates can hardly flow uniformly over the entire heat transfer area. That is, the cooling water, as shown in FIGS. 1 and 2, has its rate of flow gradually decreased as it approaches the upper edge of the heat transfer area, so that the width of the major flow is narrowed, creating a dead space. As a result, the flow rate in the upper region is increased, causing an increased pressure loss. Further, such dead space decreases the amount of heat transfer, lowering the rate of heat transfer.